Of course, you're assuming that a Centauri year is the same as our year.
The speed of light is constant...but defined by us by our own 12-month year.
For instance, in one episode, we mention that B5 is 12 of our light years from
the Narn homeworld, which is equal to about 10 of their years.

So without knowing the Centauri year, the figures are faulty.

jms